Necropsy findings and causes of loss in semi-domesticated reindeer (Rangifer tarandus tarandus) in Northern Norway

Background: Reindeer herding in Norway is based on traditional Sámi pastoralism with the animals free ranging throughout the year. The animals move over large areas in varying terrain and often in challenging weather conditions. Winter crises, such as difficult grazing conditions caused by icing or large amount of snow, are survival bottlenecks for reindeer. Calves are especially vulnerable, and many may die from starvation during winter crises. Predation and starvation are the predominant narrative to explain losses, however, carcasses are difficult to find and often little remains after scavenging and decay. Documentation of the causes of death is therefore scarce. Results : In this study, we investigated the cause of reindeer mortality in Troms and Finnmark, Nordland and Trøndelag during 2017-2019. Necropsies (n=125) and organ investigation (n=13) were performed to document cause of death. Body condition was evaluated using visual fat score and bone marrow fat index. A wide range of causes of death was detected. The diagnosis were categorized into the following main diagnostic categories: predation (n=40), emaciation (n=35), infectious disease (n=20), trauma (n=11), feeding related disease (n=5), neoplasia (4), others (n=6) and unknown (n=17). Co-morbidities were seen in a number of diagnoses (n=16). Reindeer herders are entitled to economic compensation for reindeer killed by endangered predators, but a lack of documentation leads to a gap between the amount of compensation requested and what is awarded. An important finding of our study was that predators killed animals in good as well as poor condition during winter. Emaciation was shown to also be associated with infectious diseases, and not only attributable to winter grazing conditions. Conclusions : This study highlights the importance of examining dead reindeer to gain knowledge about why they die on winter pasture. The work presented herein also shows the feasibility and value of increased documentation of reindeer losses during winter.